Method of manufacturing semiconductor integrated circuit device

ABSTRACT

In the present invention, in the exposure to light of a memory cell array or the like of a semiconductor memory or the like, when a group of unit openings for etching the STI trench regions in which the unit openings for etching the STI trench regions each having a rectangular shape are arranged in rows and columns are transferred by the exposure onto a negative resist film, multiple exposure is appropriately used which includes a first exposure step using a first optical mask having a group of first linear openings extending in a column direction and a second exposure step using a second optical mask having a group of second linear openings extending in a row direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2009-273241 filed onDec. 1, 2009 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a technology which is effective whenapplied to a lithography technique in a method of manufacturing asemiconductor integrated circuit device (or semiconductor device).

In Japanese Unexamined Patent Publication No. Hei 5(1993)-326358 (PatentDocument 1), a technology is disclosed in which one negative resist filmis exposed to light twice using two masks having respective band-likelight shielding portions orthogonal to each other so as to prevent theshape of a corner portion of a contact hole from being rounded.

In Japanese Unexamined Patent Publication No. Hei 9(1997)-289153 (PatentDocument 2), a technology is disclosed in which, in photolithographicprocessing using a polycide gate electrode and a positive resist in apolycide pattern proximate thereto, one negative resist film is exposedto light twice using two masks having different shielding patterns so asto prevent the shape of a corner portion of the pattern from beingrounded.

In Japanese Unexamined Patent Publication No. Hei 11(1999)-121701(Patent Document 3), a technology is disclosed in which, in associationwith photolithography of a Shallow Trench Isolation (STI) region of aNOR-type semiconductor memory device, to avoid an end portion of arectangular pattern from being rounded due to a proximity effect, asilicon substrate is dry-etched using a hard mask pattern and aline-and-space pattern formed of resist films orthogonal thereto as anetching-resistant mask, and thereby formed with trenches.

In Japanese Unexamined Patent Publication No. 2006-49737 (PatentDocument 4) or US Patent Publication No. 2009-122609 (Patent Document 5)corresponding thereto, a technology is disclosed in which, in a flashmemory having a split-gate flash memory cell having a Metal OxideNitride Oxide Semiconductor (MONOS) structure or a Silicon Oxide NitrideOxide Silicon (SONOS) structure, write disturb applied to a non-selectedmemory cell adjacent to a write selected memory cell via a source regionis prevented.

In Japanese Unexamined Patent Publication No. 2009-54707 (PatentDocument 6) or US Patent Publication No. 2009-050956 (Patent Document 7)corresponding thereto, a technology is disclosed in which, in a flashmemory having a split-gate flash memory cell using a MONOS structure ora SONOS structure, disturb resistance during writing in accordance witha Source Side Injection (SSI) method is improved.

PRIOR ART DOCUMENTS Patent Documents [Patent Document 1]

Japanese Unexamined Patent Publication No. Hei 5(1993)-326358

[Patent Document 2]

Japanese Unexamined Patent Publication No. Hei 9(1997)-289153

[Patent Document 3]

Japanese Unexamined Patent Publication No. Hei 11(1999)-121701

[Patent Document 4]

Japanese Unexamined Patent Publication No. 2006-49737

[Patent Document 5]

US Patent Publication No. 2009-122609

[Patent Document 6]

Japanese Unexamined Patent Publication No. 2009-54707

[Patent Document 7]

US Patent Publication No. 2009-050956

SUMMARY OF THE INVENTION

In a semiconductor integrated circuit device having a structure in whicha plurality of transistor cells having a common gate are arranged in anarray, in the step of patterning Shallow Trench Isolation (STI) regions,a STI pattern having a laterally elongated rectangular shape needs to beformed as a repeated pattern in a longitudinal direction. When theminimum dimension of the rectangular shape is on the same level as orshorter than an exposure wavelength (wavelength of an exposing lightbeam or electromagnetic wave), a proximity effect becomes prominent atan end portion of the rectangular shape to increase the deformation ofthe pattern. There is a concern that such pattern deformation may affectdevice parameters such as the gate width of a memory gate longitudinallytraversing the vicinity of the end portion.

The present invention has been achieved in order to solve theseproblems.

An object of the present invention is to provide a manufacturing processfor a semiconductor integrated circuit device with high reliability.

The above and other objects and novel features of the present inventionwill become apparent from a statement in the present specification andthe accompanying drawings.

The following is a brief description of the outline of a representativeaspect of the invention disclosed in the present application.

That is, in accordance with an aspect of the present invention, in theexposure to light of a memory cell array or the like of a semiconductormemory or the like, when a group of unit openings for etching STI trenchregions in which the unit openings for etching the STI trench regionseach having a rectangular shape are arranged in rows and columns aretransferred by the exposure onto a negative resist film, multipleexposure is appropriately used which includes a first exposure stepusing a first optical mask having a group of first linear openingsextending in a column direction and a second exposure step using asecond optical mask having a group of second linear openings extendingin a row direction (in which either the first exposure step or thesecond exposure step may be performed first).

The following is a brief description of effects achievable by therepresentative aspect of the invention disclosed in the presentapplication.

That is, in the exposure to light of a memory cell array or the like ofa semiconductor memory or the like, when the group of unit openings foretching the STI trench regions in which the unit openings for etchingthe STI trench regions each having a horizontally elongatedsubstantially rectangular shape are arranged in rows and columns aretransferred by the exposure onto a negative resist film, the multipleexposure is appropriately used which includes the first exposure stepusing the first optical mask having the group of first linear openingsextending in the column direction and the second exposure step using thesecond optical mask having the group of second linear openings extendingin the row direction. Therefore, it is possible to avoid a proximityeffect at an end portion of the rectangular shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial top view of a memory cell array in a split-gateflash memory having a MONOS memory structure as an example of a deviceas a target of a method of manufacturing a semiconductor integratedcircuit device in an embodiment of the present invention;

FIG. 2 is a device schematic cross-sectional view corresponding an A-A′cross section of FIG. 1;

FIG. 3 is a partial enlarged cross-sectional view of a peripheralportion R1 of an ONO film shown in FIG. 2;

FIG. 4 is a circuit structural diagram of a memory cell array in thesplit-gate flash memory shown in FIG. 1;

FIG. 5 shows an example of conditions for voltages applied to individuallines (a selection gate line, a memory gate line, a source line, and abit line) during writing, erasing, and reading to and from a selectedcell in the split-gate flash memory shown in FIG. 1;

FIG. 6 is a partial top view of a wafer illustrating mutual positionalrelations among a memory cell portion, a peripheral circuit portion, analignment target pattern, and a chip region in the split-gate flashmemory shown in FIG. 1;

FIG. 7 is a device process flow cross-sectional view corresponding to aB-B′ cross section of FIG. 6 (in which a memory cell array portionfurther corresponds to an A-A″ cross section of FIG. 1, and the sameapplies to the subsequent drawings of FIGS. 8 to 29) (in the step ofdepositing a silicon nitride film for processing STI regions);

FIG. 8 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of coating a resist filmfor processing the STI regions);

FIG. 9 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of patterning the resistfilm for processing the STI regions);

FIG. 10 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of filling and planarizingthe STI regions);

FIG. 11 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of introducing a P-typewell);

FIG. 12 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of introducing an N-typewell);

FIG. 13 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the steps of gate oxidation, anddepositing a first polysilicon layer);

FIG. 14 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of depositing a capinsulating film);

FIG. 15 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of coating a resist forprocessing gate electrodes in the memory cell portion);

FIG. 16 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of processing the gateelectrodes in the memory cell portion);

FIG. 17 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of removing the capinsulating film in the peripheral circuit portion);

FIG. 18 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of depositing the ONO filmand a second polysilicon layer);

FIG. 19 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of etching the secondpolysilicon layer by self-alignment);

FIG. 20 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of patterning a resistfilm for processing the ONO film and the inner gate electrodes);

FIG. 21 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of etching the ONO filmand the inner gate electrodes);

FIG. 22 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of coating a resist filmfor processing a gate electrode in the peripheral circuit portion);

FIG. 23 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of processing the gateelectrode in the peripheral circuit portion);

FIG. 24 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the steps of forming sidewallspacers, and introducing source/drain regions);

FIG. 25 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of silicidation);

FIG. 26 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of depositing a siliconnitride film over a contact);

FIG. 27 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of depositing a premetalinsulating film);

FIG. 28 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of forming tungstenplugs);

FIG. 29 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of forming a first-layermetal wiring);

FIG. 30 is a mask plan view showing an example of a pattern of anoptical mask (first optical mask) in a portion corresponding to FIG. 1in the device process flow cross sections of FIGS. 8 to 10 (STI formingstep);

FIG. 31 is a mask plan view showing an example of a pattern of anoptical mask (second optical mask) in the portion corresponding to FIG.1 in the device process flow cross sections of FIGS. 8 to 10 (STIforming step);

FIG. 32 is a device top view of the portion corresponding to FIG. 1 inthe device process flow cross section of FIG. 9 (STI forming step);

FIG. 33 is a device cross-sectional view associated with an X-X′ crosssection of FIG. 32;

FIG. 34 is a device top view of the portion corresponding to FIG. 1 atthe time when a resist film is removed after the step of FIG. 31;

FIG. 35 is a device cross-sectional view associated with an X-X′ crosssection of FIG. 34;

FIG. 36 is a device top view of the portion corresponding to FIG. 1 atthe time when a liner silicon oxide film is deposited after the step ofFIG. 34;

FIG. 37 is a device top view of the portion corresponding to FIG. 1 atthe time when isolation trenches are each filled with a silicon dioxidefilm after the step of FIG. 36;

FIG. 38 is a device top view of the portion corresponding to FIG. 1 atthe time when the unneeded buried silicon dioxide film is removed bychemical mechanical polishing after the step of FIG. 37;

FIG. 39 is a device top view of the portion corresponding to FIG. 1 atthe time when a process of etching the silicon dioxide film is executedbefore a silicon nitride film is removed after the step of FIG. 38;

FIG. 40 is a device top view of the portion corresponding to FIG. 1 atthe time when a process of removing the silicon nitride film is executedafter the step of FIG. 39;

FIG. 41 is a device top view of the portion corresponding to FIG. 1 atthe time when a process of etching the silicon dioxide film (including acleaning process and the like) is executed after the silicon nitridefilm is removed after the step of FIG. 40;

FIG. 42 is a top view of a wafer portion for illustrating the layout ofthe wafer, a unit exposure region, the chip region, the alignment targetpattern, and the like in reduced projection exposure (FIG. 6 correspondsto the chip and a peripheral region R2 thereof);

FIG. 43 is an enlarged top view of a Y-direction alignment targetpattern of FIG. 42;

FIG. 44 is an enlarged top view of an X-direction alignment targetpattern of FIG. 42;

FIG. 45 is an enlarged cross-sectional view of an example of thealignment target pattern corresponding to a B-B′ cross section of FIG.44;

FIG. 46 is an enlarged cross-sectional view of another example of thealignment target pattern corresponding to the B-B′ cross section of FIG.44;

FIG. 47 is a mask plan view showing an example (when a positive resistis used) of a first optical mask for processing a hard mask for thedevice portion of FIG. 1, which is for illustrating a process of formingthe STI regions in a method of manufacturing a semiconductor device inanother embodiment of the present invention;

FIG. 48 is a plan view of a resist film pattern (first resist film)which has been exposed to light using the optical mask of FIG. 47, anddeveloped;

FIG. 49 is a device cross-sectional view corresponding to an X-X′ crosssection of FIG. 48;

FIG. 50 is a device cross-sectional view (at the time when the etchingof the hard mask is completed) subsequent to FIG. 49;

FIG. 51 is a device plan view (at the time when the removal of the firstresist film is completed) subsequent to FIG. 50;

FIG. 52 is a device cross-sectional view corresponding to an X-X′ crosssection of FIG. 51;

FIG. 53 is a device cross-sectional view (at the time when a secondresist film is coated) subsequent to FIG. 52;

FIG. 54 is a mask plan view showing an example (when a positive resistis used) of a second optical mask for the device portion of FIG. 1,which is for illustrating the process of forming the STI regions in themethod of manufacturing the semiconductor device in the anotherembodiment of the present invention;

FIG. 55 is a device plan view of a resist film pattern (second resistfilm) which has been exposed to light using the optical mask of FIG. 54,and developed, subsequently to FIG. 53;

FIG. 56 is a device cross-sectional view corresponding to an X-X′ crosssection of FIG. 55;

FIG. 57 is a device plan view (at the time when the removal of thesecond resist is completed) subsequent to FIG. 55;

FIG. 58 is a device top view of a memory cell array portioncorresponding to FIG. 1 in a NOR-type flash memory showing anotherexample of a device as the target of the method of manufacturing thesemiconductor device in each of the embodiments of the presentinvention; and

FIG. 59 is a device schematic cross-sectional view corresponding to anA-A′ cross section of FIG. 58.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Explanation of DescriptionForm, Basic Terminology, and Use Thereof in Present Invention

1. In the present invention, if necessary for the sake of convenience,the description of an embodiment may be such that the embodiment isdivided into a plurality of sections in the description thereof.However, they are by no means independent of or distinct from each otherunless particularly explicitly described otherwise, and one of theindividual parts of a single example is details, variations, and soforth of part or the whole of the others. In principle, a repeateddescription of like parts will be omitted. Each constituent element inthe embodiment is not indispensable unless particularly explicitlydescribed otherwise, unless the constituent element is theoreticallylimited to a specific number, or unless it is obvious from the contextthat the constituent element is indispensable.

Also in the present invention, when a “semiconductor device” orsemiconductor integrated circuit device” is mentioned, it primarilyrefers to various single-element transistors (active elements), and to adevice in which a resistor, a capacitor, and the like are integratedaround such a single-element transistor over a semiconductor chip or thelike (e.g., a single-crystal silicon substrate). Representative examplesof various transistors that can be shown include Metal InsulatorSemiconductor Field Effect Transistors (MISFETs) represented by a MetalOxide Semiconductor Field Effect Transistor (MOSFET). Representativeexamples of an integrated circuit structure that can be shown includeComplementary Metal Insulator Semiconductor (CMIS) integrated circuitsrepresented by a Complementary Metal Oxide Semiconductor (CMOS)integrated circuit which is a combination of an N-channel MISFET and aP-channel MISFET.

In general, a wafer process for a present-day semiconductor integratedcircuit device, i.e., Large Scale Integration (LSI) can be roughlysub-divided into a Front End of Line (FEOL) process from the loading ofa silicon wafer as a raw material to a premetal process (processincluding the formation of an interlayer insulating film between thelower end of a MI wiring layer and a gate electrode structure or thelike, the formation of a contact hole, the burying of a tungsten plug,and the like) or the like and a Back End of Line (BEOL) process startingwith the formation of the MI wiring layer, and ending at the formationof a pad opening in a final passivation film over an aluminum-based padelectrode or the like (a wafer-level packaging process is also includedin the BEOL process). In the FEOL process, a gate electrode patterningstep, a contact hole forming step, and the like are microfabricationsteps in which particularly fine fabrication is required. On the otherhand, in the BEOL process, microfabrication is particularly required inthe step of forming vias and trenches, especially in local wiring inrelatively low layers (for example, M1 to around M3 in buried wiring ofan approximately four layer structure, and M1 to around M5 in buriedwiring of an approximately ten layer structure) and the like. Note that“MN (N=1 to about 15 is normally satisfied)” represents an N-th layerwiring from the bottom, and M1 and M3 are a first-layer wiring and athird-layer wiring, respectively.

2. Likewise, even when such wording as “X comprised of A” is used inassociation with a material, a composition, or the like in thedescription of the embodiment or the like, it does not exclude amaterial, a composition, or the like which contains an element otherthan A as one of the main constituent elements thereof unlessparticularly explicitly described otherwise, or unless it is obviousfrom the context that it excludes such a material, a composition, or thelike. For example, when a component is mentioned, the wording means “Xcontaining A as a main component” or the like. It will be appreciatedthat, even when a “silicon member” or the like is mentioned, it is notlimited to pure silicon, and a member containing a SiGe alloy, anothermulti-element alloy containing silicon as a main component, anotheradditive, or the like is also included. Likewise, it will also beappreciated that, even when a “silicon dioxide film”,“silicon-oxide-based insulating film”, or the like is mentioned, itincludes not only a relatively pure undoped silicon dioxide, but also athermal oxide film of Fluorosilicate Glass (FSG), TEOS-based siliconoxide, Silicon Oxicarbide (SiOC), Carbon-doped Silicon oxide,Organosilicate glass (OSG), Phosphorus Silicate Glass (PSG),Borophosphosilicate Glass (BPSG), or the like, a CVD oxide film, acoated silicon oxide such as Spin ON Glass (SOG) or Nano-ClusteringSilica (NCS), a silica-based Low-k insulating film (porous insulatingfilm) obtained by introducing voids into the same member as mentionedabove, a composite film with another silicon-based insulating film whichcontains any of these mentioned above as a main constituent elementthereof, and the like.

As a silicon-based insulating film commonly used in a semiconductorfield along with a silicon-oxide-based insulating film, there is asilicon-nitride-based insulating film. Materials belonging to thissystem include SiN, SiCN, SiNH, SiCNH, and the like. Here, when “siliconnitride” is mentioned, it includes both of SiN and SiNH unlessparticularly explicitly described otherwise. Likewise, when “SiCN” ismentioned, it includes both of SiCN and SiCNH unless particularlyexplicitly described otherwise.

SiC has properties similar to those of SiN but, in most cases, SiONshould rather be categorized into a silicon-oxide-based insulating film.

Silicon nitride films are not only greatly used as etch stop films in aSelf-Aligned Contact (SAC) technology, but also as stress applying filmsin a Stress Memorization Technology (SMT).

Likewise, when “nickel silicide” is mentioned, it typically refers tonickel monosilicide, but includes not only relatively pure nickelmonosilicide but also an alloy, a mixed crystal, and the like eachcontaining nickel monosilicide as a main component. Also, silicide isnot limited to nickel silicide, and may be conventionally used cobaltsilicide, titanium silicide, tungsten silicide, or the like. As a metalfilm for silicidation, not only a nickel (Ni) film, but also a nickelalloy film such as, e.g., a Ni—Pt alloy film (alloy film of Ni and Pt),a Ni—V alloy film (alloy film of Ni and V), a Ni—Pd alloy film (alloyfilm of Ni and Pd), a Ni—Yb alloy film (alloy film of Ni and Yb), or aNi—Er alloy film (alloy film of Ni and Er) or the like can be used. Notethat such silicide containing nickel as a main metal element thereof isgenerally referred to as “nickel-based silicide”.

3. Likewise, it will also be appreciated that, although a preferredexample is shown in association with a graphical figure, a position, anattribute, or the like, the graphical figure, position, or attribute isnot strictly limited thereto unless particularly explicitly describedotherwise, or unless it is obvious from the context that the graphicalfigure, position, or attribute is strictly limited thereto.

4. Further, when a specific numerical value or numerical amount ismentioned, it may be either more or less than the specific numericalvalue unless particularly explicitly described otherwise, unless thenumerical value is theoretically limited to the number, or unless it isobvious from the context that the numeral value is limited to thenumber.

5. When a “wafer” is mentioned, it typically refers to a single-crystalsilicon wafer over which a semiconductor integrated circuit device (thesame as a semiconductor device or an electronic device) is formed, butit will be appreciated that the “wafer” also includes a composite waferof an insulating substrate and a semiconductor layer or the like, suchas an epitaxial wafer, a SOI substrate, or an LCD glass substrate.

6. When “chemical mechanical polishing” or CMP is mentioned, it includesnot only CMP using floating abrasive grains, but also CMP using fixedabrasive grains.

Detailed Description of Embodiment

Embodiments of the present invention will be further described indetail. In each of the drawings, the same or similar parts are denotedby the same or similar marks or reference numerals, and a descriptionthereof will not be repeated in principle.

In the accompanying drawings, hatching or the like may be omitted evenin a cross section when hatching or the like results in complicatedillustration or when the distinction between the section to be hatchedand a vacant space is distinct. In relation thereto, even atwo-dimensionally closed hole may have a background outline thereofomitted when it is obvious from the description or the like that thehole is two-dimensionally closed and so on. On the other hand, even aportion other than a cross section may be hatched to clearly show thatthe hatched portion is not a vacant space.

§1. Description of Basic Operation of Split-Gate Flash Memory UsingMONOS Structure or SONOS Structure as Example of Device as Target ofMethod of Manufacturing Semiconductor Integrated Circuit Device inEmbodiment of Present Invention, etc. (Mainly Using FIGS. 1 to 5)

Flash memories described herein are typically used as embedded memorieswhich are embedded in a Central Processing Unit (CPU), and other chipssuch as a logic circuit chip and a signal processing circuit chip.Accordingly, a wiring system is normally, e.g., a multi-layer copperdamascene wiring, but only a first-layer wiring thereof is describedherein. Note that, as a dedicated memory, a flash memory can also bemounted on an independent chip.

FIG. 1 is a partial top view of a memory cell array in a split-gateflash memory having a MONOS memory structure as an example of a deviceas a target of a method of manufacturing a semiconductor integratedcircuit device in an embodiment of the present invention. FIG. 2 is adevice schematic cross-sectional view corresponding an A-A′ crosssection of FIG. 1. FIG. 3 is a partial enlarged cross-sectional view ofa peripheral portion R1 of an ONO film shown in FIG. 2. FIG. 4 is acircuit structural diagram of a memory cell array in the split-gateflash memory shown in FIG. 1. FIG. 5 shows an example of conditions forvoltages applied to individual lines (a selection gate line, a memorygate line, a source line, and a bit line) during writing, erasing, andreading to and from a selected cell in the split-gate flash memory shownin FIG. 1.

First, an example of a structure of a split-gate MONOS memory cell whichis a device as the target of the method of manufacturing thesemiconductor integrated circuit device in the embodiment of the presentinvention will be described using FIGS. 1 to 3. Based on the drawings, adescription will be given of a memory cell structure of the split-gateflash memory using a MONOS structure or a SONOS structure as an exampleof the device as the target of the method of manufacturing thesemiconductor integrated circuit device in the embodiment of the presentinvention, a basic structure of the memory cell array thereof, and abasic operation thereof.

First, a structure of a memory cell portion 3 (memory cell array) willbe described. The memory cell portion 3 has a two-dimensional repeatedstructure having a memory-cell repeated unit region 3 u as a unit cellor a unit lattice. As shown in FIGS. 1 to 3, a semiconductor substrate 1is comprised of, e.g., p-type single-crystal silicon, and a p-well 11 isformed therein through introduction of a p-type impurity at aconcentration higher than that of the substrate portion. In an activeregion of a first main surface 1 a (device formation surface, i.e., asurface opposite to a back surface 1 b) of the semiconductor substrate1, an n-channel MISFET (QS) for selecting a memory cell and an n-channelMISFET (QM) for a memory purpose are arranged. A drain region 9 andsource regions 8 a and 8 b of the memory cell have, e.g., relativelylow-concentration n⁻-type semiconductor regions 14 d and 14 s (which arerespectively an N-type drain extension region and an N-type sourceextension region), and a relatively high-concentration n⁺-typesemiconductor region 12 (N-type high-concentration region) having arelatively high impurity concentration higher than those of the n⁻-typesemiconductor regions 14 d and 14 s (Lightly Doped Drain (LDD)structure). The n⁻-type semiconductor regions 14 d and 14 s are disposedcloser to the channel region of the memory cell, while the n⁺-typesemiconductor region 12 is disposed at a position away from the channelregion of the memory cell by a distance corresponding to the n⁻-typesemiconductor regions 14 d and 14 s. Over the n⁺-type semiconductorregion 12, a silicide layer 15 a (over source/drain regions) such as anickel silicide layer is provided.

Over the main surface 1 a of the semiconductor substrate 1 between thedrain region 9 and the source regions 8 a and 8 b, selection gateelectrodes 6 a and 6 b of the selection re-channel MISFET (QS) describedabove, i.e., a selection transistor and memory gate electrodes 7 a and 7b of the memory n-channel MISFET (QM) described above, i.e., a memorytransistor extend in adjacent relation, and a plurality of memory cellslie adjacent to each other in the extending direction thereof viaisolation portions 5 a, 5 b, 5 c, 5 d, 5 e, and 5 f (STI regions). Thatis, a pair of word lines 6 a and 6 b longitudinally traverse, atpredetermined space intervals, each row of a group of the STI regionsarranged in a matrix.

In the same manner as over the source/drain regions and as describedabove, over the memory gate electrodes 7 a and 7 b, silicide layers 15 bsuch as nickel silicide layers are provided. Over the selection gateelectrodes 6 a and 6 b, cap insulating films 19 are provided. Inaddition, outside the memory gate electrodes 7 a and 7 b and inside theselection gate electrodes 6 a and 6 b, sidewall spacers 18 are provided.

Between the selection gate electrodes 6 a and 6 b and the main surfaceof the semiconductor substrate 1, gate insulating films 16 eachcomprised of, e.g., a thin silicon dioxide film having a thickness ofabout 1 to 5 nm are provided. As each of the gate insulating films 16,not only a silicon dioxide film, but also a silicon oxynitride film or ametal oxide film having a dielectric constant higher than that of asilicon nitride film such as a hafnium dioxide film, an aluminum oxide(alumina) film, or a tantalum oxide film may be used.

The memory gate electrodes 7 a and 7 b are provided in sidewall shapesover respective one side surfaces of multilayer films comprised of theselection gate electrodes 6 a and 6 b and the cap insulating films 19.By charge accumulation insulating films 17 (ONO films) in each of whicha lower-layer insulating film 17 a (insulating film in a layer under acharge accumulation film), a charge accumulation layer 17 b (chargeaccumulation film), and an upper-layer insulating film 17 c (insulatingfilm in a layer over a charge accumulation film) are stacked, insulationis provided between the selection gate electrodes 6 a and 6 b and thememory gate electrodes 7 a and 7 b.

The charge accumulation layer 17 b is provided in a state verticallyinterposed between the insulating films 17 a and 17 b, comprised of,e.g., a silicon nitride film, and having a thickness of, e.g., about 5to 20 nm. A silicon nitride film is an insulating film having a discretetrap level therein, and having the function of accumulating charges atthe trap level. In the present embodiment, as an insulating film havinga trap level, a silicon nitride film 9 b is formed, but the insulatingfilm having the trap level is not limited to a silicon nitride film. Forexample, a high-dielectric-constant film having a dielectric constanthigher than that of a silicon nitride film, such as an aluminum oxide(alumina) film, a hafnium oxide film, or a tantalum oxide film, may alsobe used. Otherwise, the insulating film having the trap level may alsobe formed from a silicon nanodot. Each of the insulating films 17 a and17 c is comprised of, e.g., a silicon dioxide film or the like. Thethickness of the lower-layer insulating film 17 a is, e.g., about 1.5 to6 nm, and the thickness of the upper-layer insulating film 17 c is,e.g., about 1 to 8 nm. Each of the insulating films 17 a and 17 c canalso be formed of a silicon dioxide film containing nitrogen.

Over the selection gate electrodes 6 a and 6 b and the memory gateelectrodes 7 a and 7 b, an interlayer insulating film 21 (premetalinsulating film) comprised of a silicon nitride film and a silicondioxide film is formed. In the interlayer insulating film 21, a contacthole 10 reaching the drain region 9 is formed. To the drain region 9, afirst-layer wiring 23 extending in a second direction (row direction)intersecting the memory gate electrodes 7 a and 7 b (or the selectiongate electrodes 6 a and 6 b) extending in a first direction (columndirection) is coupled via the plug 22 (tungsten plug) buried in thecontact hole 10. The wiring 23 forms the bit line of each of the memorycells.

Due to a plan configuration as shown in FIG. 1, there is a concern that,in the patterning of the STI regions 5, 5 b, 5 d, and the like, thehorizontally elongated rectangular shapes thereof may be distorted atthe end portions 24 a and 24 b thereof due to a proximity effect or thelike to vary the gate widths of MISFETs (QS and QM) provided inproximity thereto or vary the widths of the source regions 8 between theend portions 24 a and 24 b. Therefore, in Sections 3 and 5, the problemis overcome through a process improvement.

Next, using FIG. 4, an example of an array structure of split-gate MONOSmemory cells will be described. Note that, in FIG. 4, only 2 by 4 memorycells are shown for simpler illustration.

Selection gate lines (word lines) CGL0 to CGL3 coupling the selectiongate electrodes 6 of the individual memory cells, memory gate lines MGL0to MGL3 coupling the memory gate electrodes 7, and source lines SL0 andSL1 coupling the source regions 8 each shared by the adjacent two memorycells extend in parallel in the first direction (column direction). Onthe other hand, bit lines BL0 and BL1 coupling the drain regions 9 ofthe memory cells extend in the second direction (row direction), i.e.,the direction orthogonal to the selection gate line CGL0 or the like.Note that, in principle, these lines extend in the directions mentionedabove not only in a circuit diagram, but also in a layout of theindividual memory cells or the lines. The selection gate line CGL0 orthe like may also be formed of the selection gate electrode 6 or a linecoupled to the selection gate electrode 6.

To each of the source lines SL0 and SL1 and the memory gate lines MGL0to MGL3, a high voltage is applied during writing or erasing so that avoltage boosting driver comprised of a high-breakdown-voltage MISFET iscoupled thereto. On the other hand, to each of the selection gate linesCLG0 to CGL3, only a low voltage of about 1.5 V is applied so that alow-breakdown-voltage and high-speed voltage boosting driver is coupledthereto. To each local bit line, sixteen, thirty-two, or sixty-fourmemory cells are coupled. The local bit line is coupled to a global bitline via a MISFET for selecting the local bit line. The global bit lineis coupled to a sense amplifier.

In the array structure shown in FIG. 4, each of the source lines SL0 andSL1 is independently routed, while a plurality of the memory gate linesMGL0 to MGL3 are coupled to each other to provide a common memory gateline MGL. However, it is also possible that a plurality of the sourcelines SL0 and SL1 may be coupled to each other to provide a commonsource line, and a plurality of the memory gate lines MGL0 to MGL3 maybe coupled to each other to provide a common memory gate line. Byproviding the common lines, the number of high-breakdown-voltage driversfor driving the individual lines is reduced to allow a reduction in chiparea. Conversely, it is also possible that each of the source lines SL0and SL1 and the memory gate lines MGL0 to MGL3 may be independentlyrouted. In this case, the number of the high-breakdown-voltage driversincreases, but a time during which disturb is received during writingand erasing can be reduced.

Next, an example of a memory operation (writing, erasing, and reading)of a split-gate MONOS memory cell will be described using FIG. 5. Here,the injection of electrons into the charge accumulation layer 17 b isdefined as “writing”, and the injection of holes into the chargeaccumulation layer 17 b is defined as “erasing”.

A description will be given of “writing”.

Writing is performed by a so-called SSI method. As shown in FIG. 5, avoltage Vs applied to the source region 8 of a selected cell BIT1 is setto 5 V, a voltage Vmg applied to the memory gate electrode 7 is set to10 V, and a voltage Vsg applied to the selection gate electrode 6 is setto 1 V. Then, a voltage Vd applied to the drain region 9 is controlledsuch that a channel current during writing has a given set value. Thevoltage Vd at this time is determined by the set value of the channelcurrent and the threshold voltage of the selection MISFET (QS), andbecomes about 0.4 V at a set current value of, e.g., 1 μA. A voltageVwell applied to the p-well 11 is 0 V.

Next, the movement of charges when a write voltage is applied to theselected cell BIT1 will be described. By applying a voltage higher thanthat applied to the drain region 9 to the selection gate electrode 6 tobring the selection MISFET (QS) into an ON state, and applying apositive high voltage to the source region 8, electrons flow from thedrain region 9 to the source region 8. The electrons flowing in achannel region are accelerated in the channel region (between the sourceregion 8 and the drain region 9) under the vicinity of the boundarybetween the selection gate electrode 6 and the memory gate electrode 7to become hot electrons. The hot electrons are attracted to the memorygate electrode 7 by the positive voltage applied to the memory gateelectrode 7, and injected into the charge accumulation layer 17 b underthe memory gate electrode 7. The injected hot electrons are trapped by atrap level in the charge accumulation layer 17 b, and consequently theelectrons are accumulated in the charge accumulation layer 17 b to raisethe threshold voltage of the memory n-channel MISFET (QM). Next, adescription will be given of “erasing”.

As shown in the “Erasing” column of FIG. 5, erasing is performed by BTBTerasing in which holes are generated through a Band-to-Band Tunneling(BTBT) phenomenon, and accelerated with an electric field so that hotholes are injected into the charge accumulation layer 17 b or by FNerasing in which holes are injected from the memory gate electrode 7 orthe semiconductor substrate 1 into the charge accumulation layer byFowler-Nordheim (FN) tunneling.

In the case where the BTBT erasing is performed, the voltage Vmg appliedto the memory gate electrode 7 is set to −6 V, the voltage Vs applied tothe source region 8 is set to V, and the voltage Vsg applied to theselection gate electrode 6 is set to 0 V, while the drain region 9 s isbrought into a floating state. To the p-well 11, 0 V (Vwell) is applied.When the voltages shown above are applied, holes generated at the endportion of the source region 8 by the voltage applied between the sourceregion 8 and the memory gate electrode 7 through the BTBT phenomenon areaccelerated by the high voltage applied to the source region 8 to becomehot holes, and the hot holes are attracted in the direction of thememory gate electrode 7 by the high voltage applied to the memory gateelectrode 7, and injected into the charge accumulation layer 17 b. Theinjected hot holes are trapped by the trap level in the chargeaccumulation layer 17 b so that the threshold voltage of the memoryn-channel MISFET (QM) lowers.

In the case of performing the FN erasing in which holes are injectedfrom the memory gate electrode 7, to increase the likeliness of FNtunneling injection of holes to occur, a structure is adopted in whichthe thickness of the upper-layer insulating film 17 c is adjusted to benot more than 3 nm or the upper-layer insulating film 17 c is notprovided in FIG. 3. In the case of adopting the structure with theupper-layer insulating film 17 c, to increase the likeliness of theholes to be injected, a configuration may be provided appropriately inwhich a silicon nitride film or an amorphous silicon film having athickness of about 1 nm is inserted between the memory gate electrode 7and the upper-layer insulating film 17 c. On the other hand, in the caseof adopting the structure without the upper-layer insulating film 17 c,to increase the likeliness of the holes to be injected, the chargeaccumulation layer 17 b may be provided appropriately with aconfiguration using a silicon oxynitride film or a configuration inwhich a silicon nitride film and a silicon oxynitride film are stackedin succession over the semiconductor substrate. As voltages applied forthe FN erasing in which holes are injected from the memory gateelectrode 7, the voltage Vmg applied to the memory gate electrode 7 isset to 15 V, and the other applied voltages, i.e., the voltage Vsapplied to the source region 8, the voltage Vsg applied to the selectiongate electrode 6, the voltage Vd applied to the drain region 9, and thevoltage Vwell applied to the p-well 11 are each set to 0 V. When thevoltages shown above are applied, holes are injected from the memorygate electrode 7 into the charge accumulation layer 17 b by FNtunneling. In addition, electrons accumulated in the charge accumulationlayer 17 b during writing are extracted to the memory gate electrode 7.

In the case of performing the FN erasing in which holes are injectedfrom the semiconductor substrate 1, to increase the likeliness of FNtunneling injection of holes to occur, a structure is adopted in whichthe thickness of the lower-layer insulating film 17 a is adjusted to benot more than 3 nm in the memory cell shown in FIG. 3. Alternatively, toincrease the likeliness of holes to be injected, a structure is adoptedin which a silicon nitride film or an amorphous silicon film having athickness of about 1 nm is inserted between the semiconductor substrate1 and the lower-layer insulating film 17 a. As voltages applied for theFN erasing in which holes are injected from the semiconductor substrate1, the voltage Vmg applied to the memory gate electrode 7 is set to −15V, and the other applied voltages, i.e., the voltage Vs applied to thesource region 8, the voltage Vsg applied to the selection gate electrode6, the voltage Vd applied to the drain region 9, and the voltage Vwellapplied to the p-well 11 are each set to 0 V. When the voltages shownabove are applied, holes are injected from the semiconductor substrate 1into the charge accumulation layer 17 b by tunneling. In addition,electrons accumulated in the charge accumulation layer 17 b duringwriting are extracted to the semiconductor substrate 1.

Next, a description will be given of “reading”.

As shown in the “reading” column of FIG. 5, reading is performed by twotypes of methods in which reading is performed by allowing a current toflow in a direction reverse to that for writing and in which a currentis allowed to flow in the same direction as that for writing. As shownin FIG. 5, in the case of allowing a current to flow in the directionreverse to that for writing to perform reading, the voltage Vd appliedto the drain region 9 is set to 1.5 V, the voltage Vs applied to thesource region 8 is set to 0 V, the voltage Vsg applied to the selectiongate electrode 6 is set to 1.5 V, and the voltage Vmg applied to thememory gate electrode 7 is set to 1.5 V. In the case of allowing acurrent to flow in the same direction as that for writing to performreading, the voltage Vd applied to the drain region 9 and the voltage Vsapplied to the source region 8 are switched and respectively set to 0 Vand 1.5 V.

The voltage Vmg applied to the memory gate electrode 7 during reading isset between the threshold voltage of the memory n-channel MISFET (QM) ina write state and the threshold voltage of the memory n-channel MISFET(QM) in an erase state. When the respective threshold voltages in thewrite state and the erase state are set to 4 V and −1 V, the foregoingvoltage Vmg during reading has a middle value therebetween. By settingthe voltage Vmg at the middle value, even if the threshold voltage inthe write state lowers by 2 V or the threshold voltage in the erasestate rises by 2 V during data retention, the write state or the erasestate can be recognized so that the margin of a data retention propertyincreases. If the threshold voltage of the memory cell in the erasestate is set sufficiently low, it is also possible to set the voltageVmg during reading to 0 V. By setting the voltage Vmg during reading to0 V, it is possible to avoid read disturb, i.e., fluctuations inthreshold voltage due to the application of a voltage to the memory gateelectrode MG.

§2. Description of Outline of Wafer Process in Method of ManufacturingSemiconductor Integrated Circuit Device in Embodiment of PresentInvention, etc. (Mainly Using FIGS. 6 to 29)

FIG. 6 is a partial top view of a wafer illustrating mutual positionalrelations among the memory cell portion, a peripheral circuit portion,an alignment target pattern, and a chip region in the split-gate flashmemory shown in FIG. 1. FIG. 7 is a device process flow cross-sectionalview corresponding to a B-B′ cross section of FIG. 6 (in which a memorycell array portion further corresponds to an A-A″ cross section of FIG.1, and the same applies to the subsequent drawings of FIGS. 8 to 29) (inthe step of depositing a silicon nitride film for processing the STIregions). FIG. 8 is a device process flow cross-sectional viewcorresponding to the B-B′ cross section of FIG. 6 (in the step ofcoating a resist film for processing the STI regions). FIG. 9 is adevice process flow cross-sectional view corresponding to the B-B′ crosssection of FIG. 6 (in the step of patterning the resist film forprocessing the STI regions). FIG. 10 is a device process flowcross-sectional view corresponding to the B-B′ cross section of FIG. 6(in the step of filling and planarizing the STI regions). FIG. 11 is adevice process flow cross-sectional view corresponding to the B-B′ crosssection of FIG. 6 (in the step of introducing a P-type well). FIG. 12 isa device process flow cross-sectional view corresponding to the B-B′cross section of FIG. 6 (in the step of introducing an N-type well).FIG. 13 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the steps of gate oxidation, anddepositing a first polysilicon layer). FIG. 14 is a device process flowcross-sectional view corresponding to the B-B′ cross section of FIG. 6(in the step of depositing the cap insulating film). FIG. 15 is a deviceprocess flow cross-sectional view corresponding to the B-B′ crosssection of FIG. 6 (in the step of coating a resist for processing thegate electrodes in the memory cell portion). FIG. 16 is a device processflow cross-sectional view corresponding to the B-B′ cross section ofFIG. 6 (in the step of processing the gate electrodes in the memory cellportion). FIG. 17 is a device process flow cross-sectional viewcorresponding to the B-B′ cross section of FIG. 6 (in the step ofremoving the cap insulating film in the peripheral circuit portion).FIG. 18 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of depositing the ONO filmand a second polysilicon layer). FIG. 19 is a device process flowcross-sectional view corresponding to the B-B′ cross section of FIG. 6(in the step of etching the second polysilicon layer by self-alignment).FIG. 20 is a device process flow cross-sectional view corresponding tothe B-B′ cross section of FIG. 6 (in the step of patterning a resistfilm for processing the ONO film and the inner gate electrodes). FIG. 21is a device process flow cross-sectional view corresponding to the B-B′cross section of FIG. 6 (in the step of etching the ONO film and theinner gate electrodes). FIG. 22 is a device process flow cross-sectionalview corresponding to the B-B′ cross section of FIG. 6 (in the step ofcoating a resist film for processing a gate electrode in the peripheralcircuit portion). FIG. 23 is a device process flow cross-sectional viewcorresponding to the B-B′ cross section of FIG. 6 (in the step ofprocessing the gate electrode in the peripheral circuit portion). FIG.24 is a device process flow cross-sectional view corresponding to theB-B′ cross section of FIG. 6 (in the steps of forming sidewall spacers,and introducing source/drain regions). FIG. 25 is a device process flowcross-sectional view corresponding to the B-B′ cross section of FIG. 6(in the step of silicidation). FIG. 26 is a device process flowcross-sectional view corresponding to the B-B′ cross section of FIG. 6(in the step of depositing a silicon nitride film over a contact). FIG.27 is a device process flow cross-sectional view corresponding to theB-B′ cross section of FIG. 6 (in the step of depositing a premetalinsulating film). FIG. 28 is a device process flow cross-sectional viewcorresponding to the B-B′ cross section of FIG. 6 (in the step offorming tungsten plugs). FIG. 29 is a device process flowcross-sectional view corresponding to the B-B′ cross section of FIG. 6(in the step of forming a first-layer metal wiring). Based on thedrawings, a description will be given of the outline of a wafer processin the method of manufacturing a semiconductor integrated circuit devicein an embodiment of the present invention.

First, referring to FIG. 6, a layout of a target device and the likeover a wafer 1 will be described. As shown in FIG. 6, the memory cellportion 3 (memory cell array) occupies a part of a chip region 2. Thechip region 2 is a product circuit region where an actual productcircuit is formed. In the vicinity of the memory cell portion 3, amemory peripheral circuit 4 having a CMOS or CMIS structure is normallyprovided. In a scribe region 64 outside the chip region 2, an alignmenttarget pattern 25 is placed. The alignment target pattern 25 includes anX-direction alignment target pattern 25 x, a Y-direction alignmenttarget pattern 25 y, and the like. Next, using device cross sectionscorresponding to the B-B′ cross section of FIG. 6 (in which the memorycell array portion further corresponds to the A-A″ cross section of FIG.1), the outline of the wafer process will be described. Note that,because of illustrative limitations, each of the cross sections shownbelow depicts a part of each of the memory cell portion 3, the memoryperipheral circuit 4, the X-direction alignment target pattern 25 x, andthe like. Of the memory peripheral circuit 4, a part of the P-channelportion having the CMOS or CMIS structure is shown.

As shown in FIG. 7, respective cross sections correspond to the memorycell array 3, the peripheral circuit portion 4, and the alignment targetpattern portion 25 arranged from left to right. As a starting material,the wafer 1 is prepared. Examples of the wafer 1 that can be showninclude a P-type single-crystal silicon wafer (silicon-basedsingle-crystal wafer) and the like. Note that the wafer 1 may be eitheran epitaxial wafer or a SOI wafer. Examples of the wafer 1 that can beshown in terms of the size thereof include a 300φ wafer (having asubstantially circular shape of a diameter of about 300 mm). Note that,in addition thereto, a 200φ wafer, a 450φ wafer, and the like can alsobe shown as the examples thereof. The process steps will be describedhereinbelow.

As shown in FIG. 7, over substantially the entire first main surface 1 a(opposite to the back surface 1 b) of the wafer 1, a silicon dioxidefilm (pad silicon oxide film) 26 having a thickness of, e.g., about 10nm is formed first by thermal oxidation. As a thermal oxidation process,a single-wafer lamp heating method (which may also be a batch process)in, e.g., a hydrogen/oxygen mixed gas atmosphere under reduced pressureor the like may be used appropriately (hereinafter referred to as“H₂/O₂-mixed-gas-atmosphere reduced-pressure oxidation”). The padsilicon oxide film 26 is formed to protect the wafer 1 from etchingdamage when the STI regions are processed. Subsequently, oversubstantially the entire surface of the pad silicon oxide film 26, asilicon nitride film 27 for processing the STI regions having athickness of, e.g., about 90 nm is deposited by a Chemical VaporDeposition (CVD) method or the like.

Next, as shown in FIG. 8, a resist film 28 for processing the STIregions is coated over substantially the entire surface of the siliconnitride film 27. Subsequently, the wafer 1 over which the resist film 28for processing the STI regions is coated is processed by a lithographyprocess or the like in Section 3 or 4. Here, by way of example, only theoutline of the step of forming the STI regions is describedcorrespondingly to Section 3 (see Section 3 for the details thereof).

That is, by the method shown in Section 3, the resist film 28 isdeveloped to result in a state as shown in FIG. 9. Subsequently, in astate where there is the patterned resist film 28, anisotropic dryetching is executed to etch the silicon film 27, the pad silicon oxidefilm 26, and the first main surface 1 a (surface region of a siliconmember) of the wafer 1, and form isolation trenches. Thereafter, theresist film 28 is removed. Further, over the main surface 1 a of thewafer 1 and in the isolation trenches, a buried insulating film 5 isdeposited by, e.g., a CVD method or the like.

Subsequently, the first main surface 1 a of the wafer 1 is planarized bya Chemical Mechanical Polishing (CMP) method or the like to result in astate as shown in FIG. 10, whereby the STI regions 5 (group of STIregions arranged in a matrix) and the target pattern 25 are completed.In FIG. 10, for ease of description, the X-direction alignment targetpattern 25 x is shown by way of example. However, at the same time asthe STI regions 5 (group of STI regions arranged in a matrix) and thetarget pattern 25 x are formed, the Y-direction alignment target pattern25 y is also formed. Next, as shown in FIG. 11, in a state where theportions other than the memory cell portion 3 are covered with a resistfilm 29 for P-well introduction, the P-well 11 is formed in the memorycell portion 3 by ion implantation.

Next, as shown in FIG. 12, in a state where the portions other than theperipheral circuit portion 4 are covered with a resist film 31 forN-well introduction, an N-well 32 is formed by ion implantation.Thereafter, the resist film 31 is removed.

Next, as shown in FIG. 13, over the first main surface la of the wafer1, the gate insulating film 16 having a thickness of, e.g., about 7 nmis formed by, e.g., the H₂/O₂-mixed-gas-atmosphere reduced-pressureoxidation. Further, over the gate insulating film 16, a first-layerpolysilicon film 33 having a thickness of, e.g., about 140 nm isdeposited by, e.g., a CVD method or the like.

Next, as shown in FIG. 14, over the first-layer polysilicon film 33, thecap insulating film 19 comprised of, e.g., a lower-layer cap siliconoxide film 19 a (having a thickness of, e.g., about 10 nm) and anupper-layer cap silicon nitride film 19 b (having a thickness of, e.g.,about 50 nm) is deposited by, e.g., a CVD method or the like.

Next, as shown in FIG. 15, over the cap insulating film 19, a resistfilm 34 for patterning selection gates is coated. Subsequently, thewafer 1 over which the resist film 34 is coated is introduced into alithography apparatus (including an exposure apparatus) and, using theX-direction alignment target pattern 25 x, alignment in the X-direction(row direction) is executed. Likewise, using the Y-direction alignmenttarget pattern 25 y, alignment in the Y-direction (column direction) isexecuted and, using an optical mask, selective exposure to light of thememory cell portion 3 is performed (in other words, using theX-direction alignment target pattern 25 x and the Y-direction alignmenttarget pattern 25 y each transferred using the mask of FIG. 30 describedin Section 3, alignment in the X-direction and the Y-direction isexecuted). This means that alignment during the patterning of theselection gates is executed using the positions in the X-direction ofthe group of STI regions arranged in a matrix as a reference.Accordingly, as shown in FIG. 1, it is possible to minimize, e.g., thedisplacement in the X direction (row direction) between the end portion24 a of the STI region 5 b and the selection gate electrode 6 a.

Here, if it is assumed that a positive resist, e.g., is used, the resistin the peripheral circuit portion 4 is not basically exposed to light,while the resist over the alignment target pattern 25 is substantiallyentirely exposed to light. After the exposure is thus performed, theresist film 34 is subjected to a development process.

Using the patterned resist film 34 as a mask, anisotropic dry etching isexecuted to result in a state as shown in FIG. 16. That is, a multilayerfilm comprised of the selection gate electrode 6 a and the capinsulating film and a multilayer film comprised of the selection gateelectrode 6 b and the cap insulating film 19 are formed. Thereafter, theresist film 34 is removed.

Next, as shown in FIG. 17, when the cap insulating film 19 b formed overthe first-layer polysilicon film 33 in the peripheral circuit portion 4is removed, in a state where the portions other than the peripheralcircuit portion 4 is covered with a resist film 35, wet etching (using,e.g., a hot-phosphoric-acid-based silicon nitride film etchant and ahydrofluoric-acid-based silicon dioxide film etchant) is executed to thefirst main surface 1 a of the wafer 1, thereby removing the capinsulating film 19 b in the peripheral circuit portion 4. In the step ofremoving the cap insulating film 19 b, the cap insulating film 19 a isused as an etching stopper. Thereafter, the resist film 35 is removed.The cap insulating film 19 a formed in the peripheral circuit portion 4is subjected to the subsequent cleaning step or the like, and removed.

Next, as shown in FIG. 18, the Oxide Nitride Oxide (ONO) film 17 isdeposited over substantially the entire first main surface 1 a of thewafer 1 by, e.g., a CVD method or the like. Subsequently, oversubstantially the entire main surface 1 a of the wafer 1, a second-layerpolysilicon film 36 having a thickness of, e.g., about 50 nm isdeposited by, e.g., a CVD method or the like.

Next, as shown in FIG. 19, anisotropic dry etching is executed tosubstantially the entire first main surface 1 a of the wafer 1 to leave,into sidewall shapes, the second-layer polysilicon film 36 a part ofwhich is to serve as the memory gate electrodes 7 a and 7 b onrespective both sides of the multilayer film comprised of the selectiongate electrode 6 a and the cap insulating film 19 and the multilayerfilm comprised of the selection gate electrode 6 b and the capinsulating film 19.

Next, as shown in FIG. 20, in a state where a part of each of the pairof selection gate electrodes 6 a and 6 b in the memory cell portion 3,the memory gate electrodes 7 a and 7 b to be left therein, theperipheral circuit portion 4, and the alignment target pattern portion25 are covered with a resist film 37, isotropic dry etching ofpolysilicon is successively executed to remove the exposed second-layerpolysilicon film 36. Then, after the resist film 37 is removed, wetetching of the silicon dioxide film, the silicon nitride film, and thelike is executed to remove the exposed ONO film 17, resulting in a stateas shown in FIG. 21. In this manner, the first and second electrodelines 7 a and 7 b are formed by self-alignment along the pair of wordlines 6 a and 6 b.

Next, as shown in FIG. 22, a resist film 38 for processing a memoryperipheral circuit gate is coated over substantially the entire firstmain surface 1 a of the wafer 1. Subsequently, the wafer 1 over whichthe resist film 38 is coated is introduced into a lithography apparatus(including an exposure apparatus) and, using the X-direction alignmenttarget pattern 25 x and the Y-direction alignment target pattern 25 y(in other words, the target pattern transferred by exposure using theoptical mask of FIG. 30 described in Section 3), alignment in theX-direction (row) direction and the Y-direction (column direction) isexecuted and, using the optical mask, selective exposure to light of theperipheral circuit portion 4 is performed. If it is assumed that apositive resist, e.g., is used, the resist in the memory cell portion 3and over the alignment target pattern 25 is not basically exposed tolight. After the exposure is thus performed, the resist film 38 issubjected to a development process. Here, the description has been givenof the case where the X-direction alignment target pattern 25 x and theY-direction alignment target pattern 25 y each used during thepatterning of the selection gate electrodes 6 are also used during thepatterning of an electrode 6 c to be formed in the peripheral circuitportion 4. In this case, for the exposure to light of the STI regions 5in the peripheral circuit portion 4, it is preferable to use a targetpattern transferred by exposure using the optical mask of FIG. 30.However, for the exposure to light of the STI regions 5 in theperipheral circuit portion, a target pattern transferred by exposureusing the optical mask of FIG. 31 can also be used. In that case, it ispreferable that, in addition to the X-direction alignment target pattern25 x and the Y-direction alignment target pattern 25 y, an X-directionalignment target pattern and a Y-direction alignment target pattern eachused during the patterning of the electrode 6 c to be formed in theperipheral circuit portion 4 are further formed using the optical maskof FIG. 31.

Next, as shown in FIG. 23, using the patterned resist film 38 as a mask,anisotropic dry etching is executed to form the gate electrode 6 c inthe peripheral circuit portion 4. Thereafter, the resist film 38 isremoved.

Next, referring to FIG. 24, a description will be given of the formationof the sidewall spacers 18 and the introduction of the source/drainregions into the individual portions by ion implantation. As shown inFIG. 24, prior to the formation of the sidewall spacers 18, the N-typedrain extension region 14 d, the N-type source extension regions 14 s,P-type extension regions 41, and the like are successively introduced.Then, over substantially the entire main surface 1 a of the wafer 1, asilicon dioxide film is deposited as an insulating film by, e.g., a CVDmethod or the like. Thereafter, anisotropic dry etching is executed toform the sidewall spacers 18. Subsequently, P-type high-concentrationregions 42, the N-type high-concentration regions 12, and the like aresuccessively introduced. Here, as an insulating film for forming thesidewall spacers, a silicon dioxide film is used, but the insulatingfilm for forming the sidewall spacers is not limited to the silicondioxide film. The sidewall spacers can also be formed of a siliconnitride film or a multilayer film of a silicon dioxide film and asilicon nitride film.

Next, as shown in FIG. 25, as the silicide layers 15 a (over thesource/drain regions) and the silicide layers 15 b (over the memorygates), nickel silicide layers, e.g., are formed. As the silicide layers15 b, besides nickel silicide layers, cobalt silicide layers, titaniumsilicide layers, or nickel silicide layers containing platinum may alsobe formed.

Next, as shown in FIG. 26, over substantially the entire first mainsurface 1 a of the wafer 1, a silicon nitride film 21 a (having athickness of, e.g., about 40 nm), which is a part of the premetalinsulating film 21, is deposited by, e.g., a DVD method or the like.

Next, as shown in FIG. 27, over substantially the entire main surface 1a of the wafer 1, an ozone-TEOS-silicon-oxide-based film 21 b (having athickness of, e.g., about 170 nm) and a plasma-TEOS-silicon-oxide-basedfilm 21 c (having a thickness of, e.g., about 100 nm), each of which isa part of the premetal insulating film 21, are successively deposited.Subsequently, as necessary, planarization by a CMP process is executed.It is also possible that a plasma-TEOS-silicon-oxide-based film, e.g.,may be further formed.

Next, as shown in FIG. 28, contact holes are formed, and the tungstenplugs 22 are buried therein via barrier metal films of titanium andtitanium nitride or the like.

Next, as shown in FIG. 29, the first-layer copper buried wiring 23 (bitlines) is formed by a single damascene method. Thereafter, the requirednumbers of wiring layers and interlayer insulating films are stacked tocomplete the device.

§3. Description of Process (Multiple Exposure Process) of Forming STIRegions in Method of Manufacturing Semiconductor Integrated CircuitDevice in Embodiment of Present Invention, etc. (Mainly Using FIGS. 30to 41)

FIG. 30 is a mask plan view showing an example of a pattern of anoptical mask (first optical mask) in a portion corresponding to FIG. 1in the device process flow cross sections of FIGS. 8 to 10 (STI formingstep). FIG. 31 is a mask plan view showing an example of a pattern of anoptical mask (second optical mask) in the portion corresponding to FIG.1 in the device process flow cross sections of FIGS. 8 to 10 (STIforming step). FIG. 32 is a device top view of the portion correspondingto FIG. 1 in the device process flow cross section of FIG. 9 (STIforming step). FIG. 33 is a device cross-sectional view associated withan X-X′ cross section of FIG. 32. FIG. 34 is a device top view of theportion corresponding to FIG. 1 at the time when a resist film isremoved after the step of FIG. 31. FIG. 35 is a device cross-sectionalview associated with an X-X′ cross section of FIG. 34. FIG. 36 is adevice top view of the portion corresponding to FIG. 1 at the time whena liner silicon oxide film is deposited after the step of FIG. 34. FIG.37 is a device top view of the portion corresponding to FIG. 1 at thetime when isolation trenches are each filled with a silicon dioxide filmafter the step of FIG. 36. FIG. 38 is a device top view of the portioncorresponding to FIG. 1 at the time when the unneeded buried silicondioxide film is removed by chemical mechanical polishing after the stepof FIG. 37. FIG. 39 is a device top view of the portion corresponding toFIG. 1 at the time when a process of etching the silicon dioxide film isexecuted before a silicon nitride film is removed after the step of FIG.38. FIG. 40 is a device top view of the portion corresponding to FIG. 1at the time when a process of removing the silicon nitride film isexecuted after the step of FIG. 39. FIG. 41 is a device top view of theportion corresponding to FIG. 1 at the time when a process of etchingthe silicon dioxide film (including a cleaning process and the like) isexecuted after the silicon nitride film is removed after the step ofFIG. 40. Based on the drawings, a description will be given of theprocess (multiple exposure process) of forming the STI regions in themethod of manufacturing the semiconductor integrated circuit device inthe embodiment of the present invention.

In the state of FIG. 8 described in Section 2, the wafer 1 is introducedinto a reduced projection exposure apparatus and, using a first opticalmask 43 and a second optical mask 46 as shown in FIGS. 30 and 31, theresist film 28 for processing the STI regions (which is a negativeresist film herein) is exposed to light in the order of, e.g., figurenumbers. That is, without interposing a development step betweenindividual exposure steps, two exposure steps are performed continuouslyusing the first optical mask 43 and the second optical mask 46. Notethat the order of the exposure steps may be inverted. In the firstoptical mask 43, a group of first linear openings 44 and mask lightshielding portions 45 defining the first linear openings 44 areprovided. On the other hand, in the second optical mask 46, a group ofsecond linear openings 47 and the mask light shielding portions 45defining the second linear openings 47 are provided. When the resistfilm 28 is developed, a pattern as shown in FIG. 32 is obtained. Thatis, in the resist film 28, a plurality of unit openings 48 each having asubstantially rectangular shape longer in the row direction than in thecolumn direction are formed in a matrix arranged in the column directionand the row direction. Thus, the exposure steps are performed using therespective two optical masks 43 and 46, and a pattern as shown in FIG.32 is produced from the resist film 28 by the subsequent development.Therefore, it is necessary for the resist film 28 used in Section 3 tobe a negative resist film.

Next, as shown in FIG. 33, in a state where there is the developedresist film 28, an anisotropic dry etching process is executed to thesilicon nitride film 27 for processing the STI regions, the pad siliconoxide film 26, and the silicon surface region of the first main surface1 a of the wafer 1 so that the STI regions 5, i.e., isolation trenchesare formed. By thus performing the exposure steps in the two orthogonaldirections using the masks for the respective directions, a proximityeffect at an end portion of each of the rectangular shapes can beavoided, and the end portion of the rectangular shape can be avoidedfrom being rounded. This is because, in the present embodiment, duringthe formation of the STI regions 5, the two exposure steps are performedusing the respective two linear masks having no corner portion to formthe resist film 28 having a rectangular shape. Because the linear maskshave no end portion or no corner portion, they are free from theinfluence of the proximity effect. When the end portions of therectangular shapes are rounded, the memory gate electrodes 7 are formedundesirably over the rounded areas of the STI regions 5, which resultsin a concern that the characteristics of the memory cells fluctuate.However, according to the present embodiment, it is possible to avoidsuch fluctuations in the characteristics of the memory cells. Inaddition, there is no need to ensure a margin considering roundness, andthe memory cell region can be reduced in size. When the resist film 28is removed, states as shown in FIGS. 34 and 35 are provided. Note thatthe patterning of the STI regions 5 in the peripheral circuit portion 4may be performed in the same manner as in the memory cell portion 3 but,in general, if the patterning is executed using either one of theoptical masks of FIGS. 30 and 31, a simpler process is achieved. In themethod described in Section 5, the patterning of the STI regions 5 inthe peripheral circuit portion 4 may be performed in the same manner asin the memory cell portion 3 but, in general, if the patterning isexecuted using either one of the optical masks of FIGS. 47 and 54, asimpler process is achieved. In the case with the method described inSection 5, if consideration is given to compatibility with the otherportions, the use of the optical mask of FIG. 54 is most preferred.

Next, as shown in FIG. 36, by subjecting the inner surfaces of theexposed isolation trenches 5 to a thermal oxidation process, linersilicon oxide films 49 are formed. Note that the thermal oxidationprocess may also be the H₂/O₂-mixed-gas-atmosphere reduced-pressureoxidation described above. In that case, the surface of the siliconnitride film 27 for processing the STI regions is also oxidized.

Next, as shown in FIG. 37, over substantially the entire main surface 1a of the wafer 1, the buried insulating film 5 such as, e.g., a silicondioxide film is deposited by, e.g., a CVD method using a High DensityPlasma (HDP).

Next, as shown in FIG. 38, to the first main surface 1 a of the wafer 1,a CMP process is executed using the silicon nitride film 27 as astopper. Then, as shown in FIG. 39, the exposed excess buried insulatingfilm 5 is etched back using a hydrofluoric-acid-based etchant.Subsequently, as shown in FIG. 40, the silicon nitride film 27 isremoved using a hot phosphoric acid or the like. Further, by executing asurface cleaning process using a hydrofluoric-acid-based etchant, thepad silicon oxide film 26 and the surface layer of the buried insulatingfilm 5 are removed, resulting in a state as shown in FIG. 41. This isexactly the state of FIG. 10 described in Section 2.

§4. Description of Alignment Target Pattern Used in Exposure Step inMethod of Manufacturing Semiconductor Integrated Circuit Device inEmbodiment of Present Invention, etc. (Mainly Using FIGS. 42 to 46)

FIG. 42 is a top view of a wafer portion for illustrating the layout ofthe wafer, a unit exposure region, the chip region, the alignment targetpattern, and the like in reduced projection exposure (FIG. 6 correspondsto the chip and a peripheral region R2 thereof). FIG. 43 is an enlargedtop view of the Y-direction alignment target pattern of FIG. 42. FIG. 44is an enlarged top view of the X-direction alignment target pattern ofFIG. 42. FIG. 45 is an enlarged cross-sectional view of an example ofthe alignment target pattern corresponding to a B-B′ cross section ofFIG. 44. FIG. 46 is an enlarged cross-sectional view of another exampleof the alignment target pattern corresponding to the B-B′ cross sectionof FIG. 44. Based on the drawings, a description will be given of thealignment target pattern used in an exposure process in the method ofmanufacturing the semiconductor integrated circuit device in each of theembodiments of the present invention.

In an exposure process in a lithography process used in the patterningof the STI regions described in Section 3, the patterning of the gateelectrodes, or the like, e.g., reduced projection exposure, a pluralityof the chip regions 2 are normally included in a region that can beexposed to light at a time in the exposure of the wafer 1 using anoptical mask, i.e., a unit exposure region 13 (shot region), as shown inFIG. 42. In the scribe region 64 between the plurality of chip regions2, the alignment target patterns 25 each formed of individual patternedlayers normally exist (in general, the plurality of the alignment targetpatterns 25 exist in each of the directions of unit patterned layers).During alignment in each exposure step, the proper target patterns 25each belonging to a previous process layer are normally combined into aset of those for the X- and Y-directions, and used. It is also possibleto use the target patterns belonging to different process layers for theX- and Y-directions, but it is preferred to use the target patternsformed by the same exposure step. In the present invention, as thetarget patterns used when the selection gate electrodes 6 are patterned,the X-direction alignment target patterns 25 x and the Y-directionalignment target patterns 25 y that are produced in the process offorming the STI regions are used. The X-direction alignment targetpatterns 25 x and the Y-direction alignment target patterns 25 y whenthe resist film used during the etching of the selection gate electrodes6 are preferably formed by the exposure step when the linear openings 44extending in the column direction are formed in the resist film 28. Thisis because, by the linear openings 44 extending in the column direction,the widths of the STI regions 5 in the row direction in the region wherethe memory cell array is formed are determined, and it is necessary toprescribe the positions of the selection gate electrodes 6 with respectto the widths. This can allow the memory gate electrodes 7 formed intosidewall shapes over the side walls of the selection gate electrodes 6to be avoided from being formed in the vicinity of the end portions ofthe STI regions 5, and stabilize the characteristics of the memorycells.

An overall plan view of the Y-direction alignment target pattern 25 y ofeach of the target patterns 25 formed in the process of forming the STIregions is shown in FIG. 43. In this example, each of element patterns25 e in the alignment target pattern has a rectangular shape (the sameapplies to those in the X-direction alignment target pattern 25 x), butit is not limited to the rectangular shape. The element pattern 25 e mayalso have another shape. Likewise, an overall plan view of theX-direction alignment target pattern 25 x of each of the target patterns25 formed in the process of forming the STI regions is shown in FIG. 44.The B-B′ cross section of FIG. 44 is shown in each of FIGS. 45 and 46correspondingly to FIGS. 22 and 15. Here, in FIG. 46, various filmsexist over the alignment target pattern 25, but the alignment targetpattern 25 can be optically recognized due to level differences in theinterfaces between the semiconductor substrate 1 and the elementpatterns 25 e of the alignment target pattern. However, in FIG. 45, thealignment target pattern 25 can be more clearly recognized. In FIG. 46,the STI regions have small level differences, and are in a nearly flatstate. As a result, it may be difficult to optically recognize thetarget pattern when various films are formed thereover. In that case,after the STI regions are formed, i.e., after the step shown in FIG. 10,a mask is added, such a resist film as to expose the alignment targetpattern portion 25 is formed, and then the buried insulating films 5formed in the STI regions are etched to emphasize the level differencebetween the wafer 1 and the target pattern. With the emphasized leveldifference, even when various films are formed thereafter, the formedvarious films reflect the emphasized level difference so that opticalrecognition of the target pattern is easy.

§5. Description of Process (Composite Mask Process) of Forming STIRegions in Method of Manufacturing Semiconductor Integrated CircuitDevice in Another Embodiment of Present Invention, etc. (Mainly UsingFIGS. 47 to 57)

A process of forming the STI regions described in Section 5 is avariation of the example described in Section 3. The process describedin Section 5 includes more complicated steps, but is advantageous inthat a positive resist can be used. It will be appreciated that, ifnecessary, a negative resist may also be used over either or each of themasks.

FIG. 47 is a mask plan view showing an example (when a positive resistis used) of the first optical mask for processing a hard mask for thedevice portion of FIG. 1, which is for illustrating a process of formingthe STI regions in a method of manufacturing a semiconductor device inanother embodiment of the present invention. FIG. 48 is a plan view of aresist film pattern (first resist film) which has been exposed to lightusing the optical mask of FIG. 47, and developed. FIG. 49 is a devicecross-sectional view corresponding to an X-X′ cross section of FIG. 48.FIG. 50 is a device cross-sectional view (at the time when the etchingof the hard mask is completed) subsequent to FIG. 49. FIG. 51 is adevice plan view (at the time when the removal of the first resist filmis completed) subsequent to FIG. 50. FIG. 52 is a device cross-sectionalview corresponding to an X-X′ cross section of FIG. 51. FIG. 53 is adevice cross-sectional view (at the time when a second resist film iscoated) subsequent to FIG. 52. FIG. 54 is a mask plan view showing anexample (when a positive resist is used) of a second optical mask forthe device portion of FIG. 1, which is for illustrating the process offorming the STI regions in the method of manufacturing the semiconductordevice in the another embodiment of the present invention. FIG. 55 is adevice plan view of a resist film pattern (second resist film) which hasbeen exposed to light using the optical mask of FIG. 54, and developed,subsequently to FIG. 53. FIG. 56 is a device cross-sectional viewcorresponding to an X-X′ cross section of FIG. 55. FIG. 57 is a deviceplan view (at the time when the removal of the second resist iscompleted) subsequent to FIG. 55. Based on the drawings, a descriptionwill be given of the process (composite mask process) of forming the STIregions in the method of manufacturing the semiconductor integratedcircuit device in the another embodiment of the present invention.

In the state of FIG. 7 described in Section 2, over the silicon nitridefilm 27 for processing the STI regions, a silicon-oxide-based filmhaving a thickness of, e.g., about 30 nm is deposited as a hard masksilicon oxide film 51 for processing the STI regions by, e.g., a CVDmethod or the like. The hard mask silicon oxide film 51 is used as anetching mask in the subsequent step of etching STI unit trench regions.Accordingly, in Section 5, the hard mask silicon oxide film 51 is used,but the etching mask is not limited thereto. Any etching mask may beused appropriately as long as it has a high etching selectivity to awafer made of silicon. Subsequently, in the same manner as in FIG. 8,the resist film 28 for processing the STI regions is coated over thehard mask silicon oxide film 51 for processing the STI regions.Subsequently, the wafer 1 is introduced into the reduced projectionexposure apparatus and, using the first optical mask 43 shown in FIG.47, reduced projection exposure is executed. However, in this example,the resist film 28 for processing the STI regions of FIG. 8 is a firstresist film 28 a for processing the STI regions which is a positiveresist. The first optical mask 43 includes a group of first linearshielding regions 54, mask openings 55 therebetween, and the like.

After the exposure, when the resist films 28 a is developed, the linearfirst resist films 28 a for processing the STI regions remain over thehard mask silicon oxide film 51 for processing the STI regions, as shownin FIG. 48. An X-X′ cross section thereof is shown in FIG. 49.

Next, in this state, the hard mask silicon oxide film for processing theSTI regions is patterned by, e.g., anisotropic dry etching or the likeas shown in FIG. 50, thereby forming a group of first linear films 52(FIGS. 51 and 52). Thereafter, when the first resist film 28 a isremoved, a state as shown in FIGS. 51 and 52 is provided.

Next, as shown in FIG. 53, over substantially the entire first mainsurface 1 a of the wafer 1 a, a second resist film 28 b (e.g., apositive resist) for processing the STI regions is coated. Next, asshown in FIG. 54, a second optical mask 46 including a group of secondlinear shielding regions 57, the mask openings 55 therebetween, and thelike is prepared. Subsequently, the wafer 1 over which the second resistfilm 28 b is coated is introduced into the reduced projection exposureapparatus and, using the second optical mask 46 shown in FIG. 54,reduced projection exposure is executed. After the exposure, when theresist film 28 b is developed, a group of second linear films 53 (FIG.55) are obtained.

Next, in a state where there are the group of first linear films 52 andthe group of second linear films 53 orthogonal to each other,anisotropic dry etching or the like is executed to the first mainsurface 1 a of the wafer 1 to etch the silicon nitride film 27 forprocessing the STI regions, the pad silicon oxide film 26, and thesilicon member of the surface 1 a of the wafer 1. As a result, as shownin FIGS. 55 and 56, isolation trenches 5, i.e., STI unit trench regionseach having a substantially rectangular shape longer in the rowdirection than in the column direction, and presenting a matrixconfiguration in the column direction and the row direction are formed.In the same manner as in Section 3, two exposure steps are performedusing two linear masks, and the group of first linear films and thegroup of second linear films 53 each formed thereby are used as anetching mask for the STI unit trench regions each having a rectangularshape. Therefore, the end portions of the STI regions 5 can be avoidedfrom being rounded. Additionally, in Section 5, for one of the etchingmasks for the STI unit trench regions, the group of linear films 52comprised of silicon dioxide films are used. As a result, the STIregions 5 can be formed such that the end portions thereof are lessrounded than those of the STI regions 5 formed in Section 3. However, anextra step for forming the group of linear films 52 comprised of silicondioxide films is consequently added.

Subsequently, when the resist film 28 b is removed, the upper surface ofthe wafer is in a state as shown in FIG. 57. This state corresponds toFIG. 35 in Section 3 and, thereafter, substantially the same process asin Section 3 may be continuously performed appropriately. The hard masksilicon oxide film 51 for processing the STI regions in FIG. 57 isautomatically removed by the subsequent CMP process. In Section 3, theorder of the two exposure steps for the resist film 28 is not specified.However, in Section 5, it is necessary to form the hard mask siliconoxide film 51 before the resist film 28 b is deposited. However, thehard mask silicon oxide film 51 can be used either in the columndirection or in the row direction.

§6. Description of Another Example of Device as Target of Method ofManufacturing Semiconductor Integrated Circuit Device in Each Embodimentof Present Invention, etc. (Mainly Using FIGS. 58 and 59)

A flash memory described here is typically mounted as a dedicated memoryon an independent chip, but may also be formed as an embedded memory.Here, the case where the flash memory is a dedicated memory will bespecifically described. In the case where the flash memory is adedicated memory, a wiring system is, e.g., a multilayer aluminum-basedtypical wiring 23 (FIG. 59), but only the first-layer wiring thereofwill be described herein. In Section 6, a specific description will begiven of a common-ground NOR flash memory, but the flash memory is notlimited thereto. It will be appreciated that the flash memory is widelyapplicable to a flash memory having a similar STI region pattern in amatrix configuration.

In association with the manufacturing of the target device in Section 6,the processes described in Sections 2 to 5 and the like can be executedwithout substantial modification or by applying thereto a correspondencerelationship described below.

FIG. 58 is a device top view of a memory cell array portioncorresponding to FIG. 1 in a NOR-type flash memory showing anotherexample of a device as the target of the method of manufacturing thesemiconductor device in each of the embodiments of the presentinvention. FIG. 59 is a device schematic cross-sectional viewcorresponding to an A-A′ cross section of FIG. 58. Based on thedrawings, a description will be given of another example of the deviceas the target of the method of manufacturing the semiconductorintegrated circuit device in each of the embodiments of the presentinvention. Note that, since both of the plan structure and thecross-sectional structure are similar in numerous points to those inFIGS. 1 and 2 (Section 1), the description will be given mainly of thecorrespondence relationship therebetween and different points.

As shown in FIGS. 58 and 59, the individual shapes and arrangement ofthe STI regions 5 a, 5 b, 5 c, 5 d, 5 e, and 5 f are exactly the same asthose in the example of Section 1. The largest difference from theexample of Section 1 is that the control gate electrodes 6 a and 6 b areeach formed of the second-layer polysilicon film (which is typically apolycide film). Under the control gate electrodes 6 a and 6 b, floatinggates 62 (charge accumulation gates) each formed of the first-layerpolysilicon film, and isolated correspondingly to the individual cellsare provided.

Here, since the individual shapes and arrangement of the STI regions 5a, 5 b, 5 c, 5 d, 5 e, and 5 f are exactly the same as those in theexample of Section 1, the individual processes in Sections 3 and 5 areapplicable thereto. At that time, as the control gate electrodes 6 a and6 b, control gate electrodes corresponding to the selection gateelectrodes 6 a and 6 b in Section 1 may be used appropriately.

§7. Description Related to Overall Lithography in Method ofManufacturing Semiconductor Integrated Circuit Device in Each Embodimentof Present Invention

(1) In the exposure process described in Section 3 or 5, in the case ofproducing a 65-nm technology node product (including a product with alarger minimum dimension such as a 90-nm technology node product), it ispreferable to perform exposure using a binary optical mask, an ArFexcimer laser beam (at a wavelength of 193 nm), and a non-immersionreduced exposure apparatus. This is referred to as an “ArF non-immersionexposure method). (2) On the other hand, in the case of producing 45-nmand 32-nm technology node products, it is preferable to perform exposureusing the method of (1) or a binary optical mask, an ArF excimer laserbeam (at a wavelength of 193 nm), and an immersion reduced exposureapparatus (water or a high-refractivity liquid having a refractivityhigher than that of water). The latter method is referred to as an “ArFimmersion exposure method”. (3) Further, in the case of producing 22-nm,16-nm, and 10-nm technology node products, it is preferable to performexposure using a binary optical mask and an Extreme Ultraviolet (EUV)reflective reduced projection exposure apparatus using a soft X-ray at awavelength of about 15 nm. This is referred to as an “EUV exposuremethod”. Note that, since a reflective optical mask is used in the EUVexposure method, each of the optical masks shown in the foregoingembodiments needs the following transformation. That is, lighttransmitting portions (openings) are transformed into reflectingportions, and light shielding portions are transformed into lightabsorbing portions (light attenuating portions). (4) Even when any ofthe foregoing exposure methods is used, since patterns for the STIregions are two-dimensional periodic patterns, i.e., patternsperiodically arranged in rows and columns, a halftone phase shift mask,a Levenson-type alternating phase shift mask, or a phase shift mask inanother form can be used appropriately instead of the binary opticalmask.

§8. Summary

While the invention achieved by the present inventors has beenspecifically described heretofore based on the embodiments thereof, thepresent invention is not limited thereto. It will be appreciated thatvarious modifications and changes can be made in the invention withoutdeparting from the gist thereof.

For example, in the foregoing embodiments, the specific description hasbeen given using, as an example, the flash memory having split-gateflash memory cells each using the MONOS structure or the SONOSstructure, but the present invention is not limited thereto. It will beappreciated that the present invention is applicable to an independentflash memory, a flash memory embedded in another chip, a Dynamic RandomAccess Memory (DRAM), a Static Random Access Memory (SRAM), othermemories, and the like in each of which isolation regions have similarshapes and a similar arrangement.

What is claimed is:
 1. A method of manufacturing a semiconductorintegrated circuit device, comprising the steps of: (a) forming anegative resist film over a first main surface of a wafer; (b) forming,in the resist film over a portion of the first main surface serving as amemory cell array, a plurality of unit openings each having arectangular shape longer in a row direction than in a column directioninto a matrix arranged in the column direction and the row direction;(c) after the step (b), in a state where there is the resist film,performing an etching process to the first main surface to form STItrench regions in the first main surface; (d) forming a buriedinsulating film over the first main surface so as to be buried in theSTI trench regions; and (e) performing a planarization process to theburied insulating film located outside the STI trench regions to form agroup of STI regions arranged in a matrix, wherein the step (b) includesthe sub-steps of: (b1) exposing the negative resist film to light usinga first optical mask having a group of first linear openings extendingin the column direction; (b2) exposing the negative resist film to lightusing a second optical mask having a group of second linear openingsextending in the row direction; and (b3) after the steps (b1) and (b2),developing the negative resist film to form the unit openings.
 2. Amethod of manufacturing a semiconductor integrated circuit deviceaccording to claim 1, further comprising the step of: (f) before thestep (a), forming a silicon-nitride-based film over the first mainsurface.
 3. A method of manufacturing a semiconductor integrated circuitdevice according to claim 1, further comprising the step of: (g) afterthe step (e), forming first and second word lines of the memory cellarray which vertically traverse, at predetermined space intervals, eachrow of the group of STI regions arranged in the matrix by a lithographyprocess.
 4. A method of manufacturing a semiconductor integrated circuitdevice according to claim 1, wherein the exposure to light of thenegative resist film in the peripheral circuit portion is performed ineither one of the sub-steps (b1) and (b2).
 5. A method of manufacturinga semiconductor integrated circuit device according to claim 1, whereinthe sub-step (b1) is performed either prior to the sub-step (b2) orafter the sub-step (b2).
 6. A method of manufacturing a semiconductorintegrated circuit device according to claim 2, wherein theplanarization process includes a chemical mechanical polishing step. 7.A method of manufacturing a semiconductor integrated circuit deviceaccording to claim 3, wherein, over the wafer, there is a scribed regionin which a first target pattern used for alignment in an exposure stepof the lithography process is formed, wherein, in the step (a), theresist film is formed also in the scribed region, wherein, in theexposure in the step (b1), the first target pattern is transferred bythe exposure onto the resist film in the scribe region, wherein, in thestep (c), a trench region for the first target pattern is formed in thescribe region, wherein, in the step (d), the buried insulating film isformed also in the trench region for the first target pattern, wherein,in the step (e), a planarization process is performed to the buriedinsulating film located outside the trench region for the first targetpattern to form the first target pattern, and wherein the alignment inthe exposure step during the lithography process is performed using thefirst target pattern.
 8. A method of manufacturing a semiconductorintegrated circuit device according to claim 7, further comprising thestep of: (h) after the step (g), forming first and second electrodelines along and outside the respective first and second word lines byself-alignment.
 9. A method of manufacturing a semiconductor integratedcircuit device according to claim 7, wherein the memory cell array is acell array of a NOR-type flash memory.
 10. A method of manufacturing asemiconductor integrated circuit device according to claim 8, whereinthe memory cell array is a cell array of a split-gate flash memoryhaving a charge accumulation film.